System of carrier current signaling on power lines



E. l. GREEN 1,836,114

SYSTEM OF CARRIER CURRENT SIGNALING ON POWER LINES Dec. 15, 1931.

2 SheetsSheet 1 Filed Feb. 25, 1928 limmu'itgljry U U I U Al MQ INVENTOR ZZZ 67666170 XWWL ATTORNEY E. l. GREEN Dec. 15, 1931.

SYSTEM OF CARRIER CURRENT SIGNALiNG ON POWER LINES 2Sheets-Sheet 2 Filed Feb. 25, 1928 INVENTOR EKG/ ealm ATTORNEY Patented Dec. 15, 1931 UNITED STATES PATENT OFFICE ESTILI. I. GREEN, OF EAST ORANGE, NEW JERSEY, ASSIGN OR TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK SYSTEM OF CARRIER CURRENT SIGNALING ON POWER LDVES Application filed February 25, 1928. Serial No. 257,024.

Among the objects of my invention are to provide a new and improved method and corresponding apparatus for multichannel carrier current signaling on multl-phase power lines. Another object of my invention is to utilize capacity coupling between carrier signaling apparatus and power conductors for the derivation of two metallic carrier signaling paths from a power line of three conductors. Another object of my 1nvention is to-provide for the operation of two signaling circuits on the conductors of a three-phase power transmission line without the use of a ground return. Other objects of my invention have relation to producing an approximate balance between two such signaling paths and selectively confining the different currents in the proper channels of a multi-channel carrier system. These and other objects of my invention Wlll become apparent on consideration of a limited number of examples of practice according to the invention, which I have chosen for disclosure in the following specification. It will be understood. that this specification relates principally to these particular examples of practice according to the invention and that the scope of the lnvention Wlll be indicated in the appended claims.

Referring to the drawings, Figure 1 1s a symbolic diagram ofa power transmission system with a superposed two-way carrier current telephone system embodying my invention; Fig 2 is a diagram showing a three-phase (power transmiss on system w th a superpose multiplex carrler current sig naling system; Fi 3 is an attenuation-ire quency diagram or certain filters of Fig.

2; Fig. 4 is a diagram of a system like that of Fig. 2, but modified in certain respects;

Fig. 5 is an attenuation-frequency diagram for certain filters of Fig. 4; Fig. 6 is a d1- agram for a system of independent carr er current communication two ways from an mtermediate location on a power network; and Fig. 7 is a frequency diagram for the filters of Fi .6.

A t rec-phase power transmissionsystefn is shown symbolically in F1 1 with the generating station G connecte by the three conductors 1, 2 and 3 to the distant load L. The conductors 1, 2 and 3 may also be tapped at intermediate points to supply current to other loads such as L.

Two-way telephone stations are represented at S and S, each with a transmitter T and a receiver R. The circuit from the transmitter T goes to the modulator M, where the voice currentsmodulate carrier current of frequency f generated by the generator 0, and the modulated carrier currents of basic frequency f go to the winding W of the transformer W W Each of the three condensers G G and G has one plate connected with a respective power conductor 1, 2, or 3. Connected with the remaining plates of the two condensers C and C is a band-pass filter F whose other end is connected to the terminals of the transformer winding W This bandpass filter F has its elements in balanced relation with respect to the two terminals at either end, that is, for the series elements there are equal condensers such as C on each side and for the shunt elements there are coils and condensers in parallel but arranged so that each is accessible for a tap at its midpoint, as shown at 11 and 12. Each of the coils 13 and 14 has an independent core and an independent magnetic circuit, as indicated by the closed dotted lines in the figure.

The filter that has just been described is connected at its output end through the transformer windings W and W to the demodulator D which is supplied with current of frequency f from the generator 0. The

output from the demodulator D goes to the V comprising coil 15 and condenser 16 in parallel, and these in series with the two coils 13 .and 14 and the two condensers 21 and 22, these four elements in parallel. It will be seen that on one side the shunt combinations,

such as 15, 16 are connected between the series condensers such as 2C,,,, and on the other side they are connected to the middle points of the shunt elements of the first described filter. Accordingly, the filter F is connected to the power line so as to utilize its conductors in a half phantom arrangement, that is, with the conductor 3 for one side of the circuit, and the conductors 1 and 2 in parallel for the other side of the circuit.

The band-pass filter F passes a range of frequencies corresponding toone or both of the sidebands of the frequency f Accordingly, the modulated carrier current carrying the voice waves from the transmitter T and having the basic frequency f goes through this filter F and is transmitted from left to right over the circuit consisting of the power conductor 3 on one side and the power conductors 1 and 2 in parallel on the other side.

On the other hand, at station S modulated carrier currents of basic frequency f are put on the line and the filter F at station S passes a range of frequencies corresponding to one or both of the sidebands of the frequency f From the filterF these received modulated carrier currents go through to the demodu-- lator D which reduces them to normal voice currents for delivery to the receiver R.

While the fundamental frequency for the power transmission system will be low com- 'pared to the carrier frequencies f and f these power currents are likely to have harmonics present, and such harmonics will be excluded from the station S by the filters F and F except if they happen to lie in the frequency ranges passed by-those filters. If the power lines were well balanced, having very low crosstalk between the circuit formed by conductors 1 and 2, and the circuit formed by conductor 3 and conductors 1 and 2 in parallel, then the balancing arrangements at station S in the transformers W 2 and W W would serve to keep the currents distinct in the transmitting and receiving channels. But in some cases such a high degree of linebalance cannot be expected for a three-phase power transmission system, and accordingly, an important function of the filters F and F is to aid in keeping the currents distinct and separate in the transmitting and receiving channels. This is accomplished in high degree by transmitting on a carrier current of one frequency f and receiving on another carrier current of a different frequency f and building the filters to pass the- The anti-resonant loops in the branch conductors to load L are tuned broadly to the mean frequency (f -'l-f )/2, and prevent any considerable diversion of the signaling currents to the power conductors leading to the load L.

By my invention, as embodied in the system of Fig. 1, it will be seen that I connect the carrier terminal apparatus to the power line through condensers such as C C and C and that I'get two distinct circuits for the carrier currents without employing grounds, and utilizing only the three conductors of the three-phase system. The use of some form of capacity coupling is very desirable for effecting a connection between carrier apparatus and power conductors. In the practice of my invention various forms of capacity coupling may be employed. Thusthe condensers C C and 0 may be standard condensers designed to withstand the power line voltages, they may be sections of high-voltage oil-filled power cable, or they may be formed by coupling antennae mounted in proximity to the power conductors.

Although the condensers C C and C have beenshown as forming elements of two band filters, they may be used as parts of tuned circuits for selecting the desired frequencies. I

In the modification shown in Figs. 2 and 3, the filters F and F 2 are high pass filters with their critical or cut-off frequencies so determined that they pass the carrier currents but do not pass the comparatively low frequency power currents northeir lower order harmonics. This system isadapted for multiplex telephone transmission, two terminal stations being shown each equipped with a transmitter T and a receiver R. The different transmitting channels are separated and determined by the band filters BF with respective ranges as indicated in the upper part of Fig. 3. The different frequency ranges for the different transmitters are superposed in the winding W of the repeating coil W WV and put-through the high pass filter F and through the condensers C and C to the circuit formed by the two conductors 2 and 3 of the three-phase power line.

It willbe seen that for the repeating coil W W its prima1y winding-W is connected across the power conductor 1 and the power conductors 2 and 3 in parallel. I refer to this connectiom a's half-phantom. Signal carrier currents incoming on this half-phantom'circuit go'through the condensers G on one side and C C in parallel on the other side, and through the high pass filter F and the repeating coil W -W and thence in multiple to the band filters BF, which have their pass ranges spaced apart and staggered in relation to the transmitting ranges as indicated in the lower part of Fig. 3 compared with its upper part.

It will be seen that in the system of Fig. 2

a plurality of two-way talking circuits is provided and that in all of them transmission is on the two-conductor circuit of the power system and reception is on the half-phantom circuit of the power system. Of course, this system will be reversed for the station at the opposite end of the line where the transmitted currents will be those received at the end pictured in Fig. 2' and the received currents will be those transmitted at the end pictured in Fig. 2.

In the system shown in F 1g. 2, the balance is partly depended on to keep the transmltted currents out of the receivers at the same end, and also this object is gained by the band pass filters BF and BF with their different ranges. Unlike Fig. 1, the filters 1 and F 2 of Fig. 2 do not separate the transmitted and received currents.

The use of the line balance as an aid in preventing the entrance of the transmitted currents into the receiving circuits permits the location of the transmitting bands much closer in frequency to the receiving bands than would be possible if both transmitting and receiving currents utilized the same line circuit. This results in a large increase in thenumber of carrier channels that may be provided. Obviously if the line cross-talk is sufiiciently. low, the transmitting and receiving bands may be made to coincide. I

Referring to Fig. 4, this shows two high pass filters F and F 2 with the same critical or cut-ofi frequencies determined as in the case of the high pass filters of Fig. 2. However, the two filters of Fig. 2 are physically distinct from each othe whereas in Fig. 4 certain reactances are common o both filters. Here the condensers C of filter F are utilized in pairs as the condensers on one side for the filter F also, the coils of the filter F are made in pairs and each pair connected in multiple with a corresponding coil of the filter F so that each shunt inductance of the filter F consists of a series coil such as L and the two multiple coils such as L. p In Fig. 2 the filter elements are distinct, whereas in Fig. 4 the elements of the filter F serve not only for that filter but as part of the filter F Another distinction between Fig. 4 and Fig. 2 is that instead of staggering the transmitting'and receiving ranges as in Fig. 3, these ranges are disposed as shown in Fig. 5. All transmitting through repeating coil W W is through the low pass filter LF and all receiving through the same coil is through high pass filter HF. If the power lines are well balanced, a similar carrier system can be connected through the repeating coil W W In case the line balance is not good enough to permit the use of identical frequency bands on the two circuits derived from the three power conductors, then the bands used may be staggered with respect to one another as was done in the system of Fig. 2.

Referring to Fig. 6, this shows a three phase line or network with conductors l, 2 and 3 and an intermediate station at which there may be a generator feeding the network, or a load drawing energ therefrom, represented in any case as X. uppose it is desired to maintain a two-way carrier communication channel on the line on one side of X and another independent like channel on the other side of X; this may be accomplished by the arrangement of apparatus shown in Fig. 6 with the frequencies apportioned as in Fig. 7 It will be seen that four frequency bands are involved and that transmission on one side is on the lowest of these, transmission on the opposite side is on the next higher band, reception on the said one side is on the next higher band, and reception on the said opposite side is on the highest band. Also, both transmission and reception on one side are on the circuit whose two conductors are respectively two conductors of the power line, and both transmission and reception 0n the opposite side are on the halfphantom circuit.

The invention has been described as applied with carrier apparatus used for giving signals or indications or efiects at a distance, and more specifically, in connection with the drawings, the invention has been exemplified in relation to telephone communication.

I claim:

1. A three-phase power-transmitting system comprising three coordinate power conductors, a ladder-type filter having a pair of input terminals and a pair of output terminals, one said pair being connected respectively to two of said conductors, and another filter having one of its terminals connected with the remaining conductor of said three conductors and its other terminal of the same pair connected at a neutral point with respect to the sides of the first mentioned filter.

2. A three-phase power-transmitting system comprising three'coordinate power conductors, a ladder-type filter having a pair of input terminals and a pair of output terminals, one said pair being connected respectively to two of said conductors, and another filter having one of its terminals connected with the remaining conductor of said three conductors and the remaining side of said last mentioned filter non-adjacent to said terminal being completed through the elements of the said first mentioned filter by a neutral connection with respect to the sides thereof.

3. In combination, a three-phase powertransmitting system comprising three coordinate power conductors, and in association therewith three condensers, respectiveconnections from one side of each condenser to one of the conductors, a ladder-type filter having a pair of terminals connected with two of the condensers, another ladder-type filter having one terminal connected with the remaining condenser and the other side of said last mentioned filter being connected neutrally with respect to the sides of the first mentioned filter, the said condensers having the proper capacity values to form terminal series reactances of the said filters.

m In testimony whereof, I have signed my name to this specification this-24th day of February, 1928.

ESTILL I. GREEN. 

